The present invention relates to methods for the production of sulfurized diphenyloxides and compositions made therefrom. In particular, the present invention relates to methods for the production of sulfurized diphenyloxides from the reaction of diphenyloxides with elemental sulfur in the presence of a solid acid catalyst. The solid acid catalyst can be a zeolite or a catalytic amount of a Friedel-Crafts compound. Compositions made from the sulfurized diphenyloxides are useful as lubricant base stocks and additives thereto.
Sulfurized diphenyloxides are beneficial as lubricant additives, lubricant base stocks, or intermediates to lubricant base stocks. Sulfurized diphenyloxides include, for example, phenoxathiin, bis(diphenyloxide) sulfides, diphenyloxide phenoxathiin sulfides, and bis(phenoxathiin) sulfides having the structures shown below. Alkylated phenoxathiin is a high-performance synthetic lube base stock with excellent viscometrics, oxidative stability, and antiwear properties. In addition, the bis(diphenyloxide) sulfide has been reported as a high-performance fluid. 
Sulfurized diphenyloxides can be prepared from the reaction of diphenyloxide with sulfur using stoichiometric amounts of AlCl3 at low temperatures. The reaction is believed to proceed through an aromatic electrophilic substitution mechanism. The acid catalyst enhances the electrophilicity of sulfur via the formation of positively charged sulfur intermediates. These intermediates are believed to be produced by the formation of a Lewis acid-base adduct between sulfur and the Lewis acid or by the protonation of sulfur by a Bronsted acid. However, the use of stoichiometric amounts of AlCl3 does not provide an adequate commercial source of sulfurized diphenyloxides. Rather, the known process suffers from numerous drawbacks, including, for example, the use of corrosive reactants (e.g., halogenated hydrocarbons), the production of corrosive by-products (e.g., gaseous hydrochloric acid), poor selectivity (e.g., the production of significant amounts of higher sulfurized diphenyloxides, such as diphenyloxide phenoxathiin sulfide), and the need for extensive downstream separations (e.g., separation of catalyst from the product stream).
These drawbacks have negative implications for the commercial use of sulfurized diphenyloxides. The commercial use of sulfurized diphenyloxides has been hampered by the need to purify the sulfurized diphenyloxide prior to use. In particular, the presence of high concentrations of corrosive by-products has made it imperative that the sulfurized diphenyloxides be removed from the product stream prior to use. However, the purification of the sulfurized diphenyloxides is expensive and time consuming.
Accordingly, it would be highly beneficial to provide methods for the large scale production of sulfurized diphenyloxides. The method should provide for the production of sulfurized diphenyloxides in large yield without the use of highly corrosive reactants. Further, the method should produce little or no corrosive and/or undesired by-products. In addition, the method should utilize readily available reactants and be selective.
The drawbacks associated with the known method for producing sulfurized diphenyloxides is overcome, to a large extent, by methods in accordance with the present invention. The present invention provides a method for producing sulfurized diphenyloxides wherein a diphenyloxide and elemental sulfur are reacted in the presence of a solid acid catalyst. The reaction is very clean and produces little undesirable by-products. Usually, high sulfur conversion and selectivity to specific sulfurized diphenyloxides can be obtained under mild reaction conditions. The method can be used to produce sulfurized diphenyloxides in large scale and at economical prices.
In one of its aspects, the present invention relates to methods for the production of a sulfurized diphenyloxide wherein a diphenyloxide is reacted with elemental sulfur in the presence of a solid acid/oxide catalyst. In one embodiment, the diphenyloxide is alkylated prior to reaction with sulfur. Alternatively, alkylation is performed after sulfurization of the diphenyloxide. Preferably, however, the sulfurization and alkylation occur concurrently. In one embodiment, the acid catalyst comprises a molecular sieve, preferably a zeolite such as MCM-56, ZSM-5, MCM-22, MCM-68, and USY. Alternatively, the catalyst comprises a catalytic amount of a Friedel-Crafts compound, such as AlCl3. When the catalyst comprises a Friedel-Crafts compound, the reaction is preferably conducted at a temperature above about 75xc2x0 C., more preferably at a temperature above about 120xc2x0 C., and even more preferably at a temperature above about 180xc2x0 C.
In another of its aspects, the present invention relates to a composition comprising between about 40 and about 80 weight percent diphenyloxide; no more than about 15 weight percent diphenyloxide thiol; between about 5 and about 45 weight percent phenoxathiin; and between about 3 and about 50 weight percent total of bis(diphenyloxide) sulfide, diphenyloxide phenoxathiin sulfide, and bis(phenoxathiin) sulfide.
Additional features and embodiments of the present invention will become apparent to those skilled in the art in view of the ensuing disclosure and appended claims.
The present invention relates to methods for the production of sulfurized diphenyloxides. The sulfurized diphenyloxides are produced by reacting a diphenyloxide with elemental sulfur in the presence of a solid acid catalyst according to reaction Scheme 1 below. It will be appreciated by those skilled in the art that the diphenyloxide can be optionally alkylated on one or both of the phenyl groups prior to reaction with the sulfur. The methods enable the production of a variety of sulfurized diphenyloxides, including phenoxathiin, bis(diphenyloxide) sulfide, diphenyloxide phenoxathiin sulfide, and bis(phenoxathiin) sulfide. Additionally, the methods can be used to produce substituted sulfurized diphenyloxides, including alkylated phenoxathiins. 
The sulfur is in its elemental form and can be used without further purification. The sulfur can be combined with the diphenyloxide to form a saturated sulfur solution. Toward that end, the sulfur can be dissolved within a liquid solution containing the diphenyloxide. For example, an appropriate amount of sulfur can be dissolved directly in an appropriate amount of diphenyloxide to provide a diphenyloxide/sulfur solution having the desired mole ratio of diphenyloxide to sulfur. Preferably, the diphenyloxide/sulfur solution is saturated with sulfur.
The reaction between the diphenyloxide and the sulfur is carried out in the presence of solid acid catalyst. The acid catalyst can be aluminum chloride (AlCl3), BF3, AlBr3, solid zeolite, a layered catalyst, or any of a variety of other molecular sieves. Examples of suitable zeolite catalysts include MCM-56, ZSM-5, MCM-22, MCM-68, and USY. Zeolites may be used with framework metal elements other than aluminum such as, for example, boron, gallium, iron, and chromium.
When a zeolite is used, the zeolite preferably has a pore size of at least 5 xc3x85. Large pore size zeolite catalysts are usually preferred, although less highly constrained medium or intermediate pore size zeolites may also be used. Generally, the large pore size zeolites are characterized by a pore structure with a ring opening of at least about 7 xc3x85 and the medium or intermediate pore size zeolites with a ring structure of 10 membered oxygen ring systems will have a pore opening smaller than about 7 xc3x85but larger than about 5.6 xc3x85. Examples of suitable large pore size zeolites include faujasite, synthetic faujasites (zeolite X and Y), zeolite L, ZSM4, ZSM-18, ZSM-20, mordinite and offretite which are characterized by the presence of a 12-membered oxygen ring system in the molecular structure as described in Chen et al., xe2x80x9cShape-Selective Catalysis in Industrial Applicationsxe2x80x9d, Chemical Industries Vol. 36, Marcel Dekker Inc., New York, 1989. The large pore zeolites are preferably characterized by a xe2x80x9cConstraint Indexxe2x80x9d of not more than 2, in most cases not more than 1. Zeolite beta is included in this class although it may have a xe2x80x9cConstraint Indexxe2x80x9d approaching the upper limit of 2. The method for determining Constraint Index is described in U.S. Pat. No. 4,016,218 together with values for typical zeolites. The significance of the Constraint Index is described in U.S. Pat. No. 4,816,932 to which reference is made for a description of the test procedure and its interpretation.
A highly useful large pore zeolite for the production of the sulfurized diphenyloxides of the invention is zeolite Y in the ultrastable form, usually referred to as USY. Zeolite USY or zeolite Y, is a material of commerce, available from W. R. Grace and Co. and other suppliers, in large quantities as a catalyst for the cracking of petroleum. Zeolite Y may be bound with silica, alumina, silica-alumina or other metal oxides. It may typically have a SiO2xe2x88x92 to Al2O3 ratio of from 3-500, and be partially exchanged with rare earth elements, with ammonium cation or with other cations. Reference is made to Wojoiechowski, xe2x80x9cCatalytic Cracking: Catalysts, Chemistry and Kineticsxe2x80x9d, Chemical Industries Vol. 25, Marcel Dekker, New York, 1986, for a description of zeolite USY, its preparation and properties.
Examples of useful medium pore size zeolites include the pentasil zeolites such as ZSM-5, ZSM-22, ZSM-23, and ZSM-35, as well as other zeolites such as ZSM-50, ZSM-57, MCM-22, MCM-49, MCM-56, MCM-68, all of which are known materials. Zeolite MCM-22 is described, for example, in U.S. Pat. No. 4,954,325 to M. K. Rubin and P. Chu. MCM-56 is described, for example, in U.S. Pat. Nos. 5,632,697; 5,453,554; 5,557,024; 5,536,894; and 5,827,491. MCM-68 is described, for example, in U.S. application Ser. No. 09/234,544, filed Jan. 21, 1999. All of the above patents and applications are hereby incorporated by reference in their entireties.
The zeolite catalyst is optionally pretreated. Pretreatment of the catalyst flows from the discovery that zeolite catalysts which are low in moisture content, water-of-hydration content and absorbed-oxygen content consistently produce compositions that have improved color and excellent oxidative and thermal stability. Commercially obtained zeolite catalysts have been found to be relatively rich in moisture content, water-of-hydration content and absorbed-oxygen content. Reducing the moisture content, water-of-hydration content and absorbed-oxygen content of the commercially obtained zeolite catalyst by pretreatment has been found to yield a superior product.
The zeolite catalyst is pretreated by heating the solid catalyst particles for a time sufficient to lower the catalyst water content, water-of-hydration and absorbed oxygen content. Preferably and conveniently, the solid catalyst is heated in a vessel in bulk form but it is within the scope of the present invention to suspend the catalyst in an otherwise unreactive and inert liquid, with or without stirring, to enhance heat transfer to the solid catalyst and accelerate pretreatment. Vapor of the inert liquid may be removed periodically to carry off water vapor and oxygen from the catalyst. However, the zeolite catalyst is pretreated preferably by heating the solid catalyst in an inert gaseous environment at a temperature and for a time sufficient to lower the catalyst water content, water-of-hydration and absorbed oxygen content. Most preferably, the pretreatment is carried out in a vessel employing a moisture-free inert gas purge stream, such as nitrogen or Group VIII gases of the Periodic Table, to remove water vapor and oxygen from the vessel. Optionally, the pretreatment may be carried out by heating the catalyst in vacuo in a closed vessel.
To those skilled in the chemical engineering arts, other means are well known to essentially dry solid particles by continuous or batchwise methods. These methods are included within the scope of the present invention to the extent that they can be applied to remove water, water-of-hydration and absorbed oxygen from solid zeolite catalyst particles. The zeolite catalyst can be pretreated in a fixed bed, fluid bed or batchwise. Rather than employing a vessel, the solid catalyst particles can be transported through a column containing an inert liquid at an appropriate temperature or the solid can be carried through a heated or inert liquid-containing column by gas ebullition.
The water content, water-of-hydration and absorbed oxygen content of the zeolite catalyst particles can be effectively lowered by heating the catalyst at a temperature between about 50xc2x0 C. and about 500xc2x0 C., but preferably at a temperature between about 200xc2x0 C. and about 400xc2x0 C. The catalyst is heated for between about 0.5 hours and about 24 hours and, preferably, between about 1 hour and about 5 hours. However, at a preferred temperature of about 300xc2x0 C. in a vessel in the presence of a nitrogen purge stream, about two hours of heating has been found sufficient to pretreat the catalyst particles.
As an alternative to the zeolites, other molecular sieves may be used. Examples of useful, non-zeolite molecular sieves include the silicates (e.g., metallosilicates, titanosilicates) of varying silica-alumina ratios; metalloaluminates (e.g., germaniumaluminates); metallophosphates; aluminophosphates (AlPO; e.g., the silico- and metalloaluminophosphates referred to as metal integrated aluminophosphates (MeAPO and ELAPO); metal integrated silicoaluminophosphates (e.g., MeAPSO and ELAPSO); and silicoaluminophosphates (SAPO)); and gallogermanates. Without intending to be bound by theory, it is believed that use of the non-zeolite molecular sieves may not be as favorable since it appears that some acidic activity (as conventionally measured by the alpha value) is desired for optimum performance. A discussion of the structural relationships of SAPOs, AlPOs, MeAPOs, and MeAPSOs may be found in a number of resources including Stud. Surf Catal., 37:13-27 (1987). The AlPOs contain aluminum and phosphorus, while in the SAPOs some of the phosphorus and/or some of both the phosphorus and aluminum is replaced by silicon. In the MeAPOs, various metals are present, such as Li, B, Be, Mg, Ti, , Fe, Co, An, Ga, Ge, and As, in addition to aluminum and phosphorus, while the MeAPSOs additionally contain silicon. The negative charge of the MeaAlbPcSidOe lattice is compensated by cations, where Me is magnesium, manganese, cobalt, iron, and/or zinc. MeAPSOs are described in U.S. Pat. No. 4,793,984. SAPO-type sieve materials are described in U.S. Pat. No. 4,440,871. MeAPO-type catalysts are described in U.S. Pat. Nos. 4,544,143 and 4,567,029. ELAPO catalysts are described in U.S. Pat. No. 4,500,651 and ELAPSO catalysts are described in European Patent Application No. 159,624. Specific molecular sieves are described, for example, in the following patents: MgAPSO and MgAPSO in U.S. Pat. No. 4,758,419; MnAPSO in U.S. Pat. No. 4,686,092; CoAPSO in U.S. Pat. No. 4,744,970; FeAPSO in U.S. Pat. No. 4,683,217; and ZnAPSO in U.S. Pat. No. 4,935,216. All of the above patents and applications are hereby incorporated by reference in their entireties. Specific silicoaluminumphosphates which may be used include SAPO-1 1, SAPO-17, SAPO-34, and SAPO-37. Other specific sieve materials include MeAPO-5 and MeAPSO-5.
The method of the invention is carried out by contacting the diphenyloxide, sulfur, and the catalyst in a suitable reaction zone which may be a fixed catalyst bed, fluid bed or stirred reactor vessel. The mole ratio of the diphenyloxide to sulfur is preferably between about 50:1 and about 0.1:1 and, more preferably, between about 25:1 and about 10:1, to provide sufficient diluent for the reaction. A mole ratio of higher than about 50:1 detrimentally affects the reaction by dilution. If the mole ratio is below about 1:1, excess unreacted diphenyloxide may remain.
The time for which the diphenyloxide and the sulfur are contacted can vary. In general, contact is maintained for a time sufficient that the diphenyloxide and the sulfur react to a desired level of completion. For example, contacting time can vary from several minutes to several hours or more.
The temperature which is maintained during the reaction of the diphenyloxide and the sulfur can also vary. In general, it is preferred to carry out the reaction at the lowest temperature which will provide for the desired efficiency of reaction. For example, suitable temperatures can range from about 20xc2x0 C. to about 300xc2x0 C. Preferably, when a zeolite catalyst is used, the reaction is carried out at, or slightly above, ambient room temperature. xe2x80x9cRoom temperaturexe2x80x9d, as used herein, includes temperatures from about 20xc2x0 C. to about 30xc2x0 C., preferably about 25xc2x0 C. When the catalyst comprises a Friedel-Crafts compound such as AlCl3, the reaction is preferably conducted at a temperature above about 75xc2x0 C., more preferably at a temperature above about 120xc2x0 C., and even more preferably above about 180xc2x0 C.
The pressure maintained during the reaction between the diphenyloxide and the sulfur can also vary. Appropriate pressures to provide efficient formation of sulfurized diphenyloxide product can be readily determined by one of skill in the art. For example, suitable pressures can range from about ambient pressure to about autogenous reaction pressure at the selected temperature. However, higher pressures can be used, for example up to about 1000 psig (68 atm) Preferably, the pressure is between about 400 psig (27.2 atm) and about 600 psig (40.8 atm).
The fixed bed weight hourly space velocity (WHSV) can also be varied. Appropriate values for the WHSV are between about 0.0 hrxe2x88x921 and about 10 hrxe2x88x921, preferably between about 0.1 hrxe2x88x921 and about 2 hrxe2x88x921, and more preferably between about 0.1 hrxe2x88x921 and about 1 hr xe2x88x921. A WHSV above about 10 hrxe2x88x921 is detrimental because of the short residence time. A WHSV below about 0.01 hrxe2x88x921 results in low productivity.
Alkylated sulfurized diphenyloxides can be prepared by introducing an alkylating agent into the reaction zone. The alkylating agent can be present in the reaction zone before, after, or while the diphenyloxide is contacted with the sulfur. Preferably, the alkylating agent is present during the sulfurization step so that diphenyloxides are produced from diphenyloxides in a single step. The alkylating agent is preferably an olefin, more preferably a C6 to C20 olefin, and most preferably a C10 to C18 alpha olefin such as dodecene-1, decene-1, and tetradecene-1.
Once the diphenyloxide, the elemental sulfur, and the optional alkylating agent have reacted to the desired level of completion, the resulting product mixture can optionally be purified. Preferably, the catalyst is removed from the product mixture. When a zeolite catalyst is used, the catalyst can be separated from the product mixture by, for example, filtration. When a Friedel-Crafts compound such as AlCl3 is used, the catalyst can be separated by, for example, washing the product mixture with a suitable solvent (e.g., water).
The product mixture can also be treated to separate specific sulfurized diphenyloxide products from the product mixture. For example, the product mixture will generally contain a mixture of sulfurized diphenyloxides such as phenoxathiin, bis(diphenyloxide) sulfide, diphenyloxide phenoxathiin sulfide, bis(phenoxathiin) sulfide, and higher sulfurized diphenyloxides. The phenoxathiin may be separated from the other components by conventional chemical processing techniques, such as by distilling the product mixture under vacuum. The bis(diphenyloxide) sulfide, diphenyloxide phenoxathiin sulfide, and bis(phenoxathiin) sulfide can then be separated from the higher sulfurized diphenyloxides also using conventional chemical processing techniques.
If further alkylation is desired (or if alkylation has not been previously performed), the sulfurized diphenyloxides are also optionally alkylated to produce alkylated sulfurized diphenyloxides. The alkylation can be performed individually on specific diphenyloxides which have been separated from the product mixture. Alternatively, the alkylation can be performed on the product mixture as a whole to produce a mixture of alkylated sulfurized diphenyloxides.